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Rain fed lowland traditional variety rice cultivation in Andaman and Nicobar islands in acidic soils with low inherent fertility is done with minimal use of fertilizer and thus have low yields and profits. Use of hybrids and balanced fertilization especially nitrogen (N) may improve the situation. In this context, a field study was made during 2016 rainy season to assess the performance of 8 hybrids (including a variety) in main plots and four N rates (0, 50, 100 and 150 kg/ha) as sub-plot treatments. Experiment was laid out in split plot design with three replications. Results based on grain yield (t/ha) and net income (Rs/ha) revealed that rice hybrid „KPH-459‟ (3.32 t/ha and Rs. 14585) and 100 kg/ha N fertilization (3.22 t/ha and Rs.12105) as the best treatments. Cultivar and nitrogen interaction indicated that „KPH-459‟ with 50 kg N fertilization is as good as „PR-14019‟, „PR-14112‟ hybrids and better than „WGL-14‟ variety receiving highest N (150 kg) for profits. Cultivation of „KPH 459‟ hybrid with 100 kg N gave the significantly higher profits (Rs. 29607) than all other cultivars and N combinations. Nitrogen uptake followed the trend of grain yields, however all N use efficiency indices (Physiological efficiency, Apparent recovery and Utilization efficiency) except agronomic efficiency have highest values high at 50 kg N. N response of rice crop and 6 cultivars was linear (KPH-459‟ and „PR-14019‟ have quadratic response). Replacement of current rice varieties with „KPH459‟ hybrid with high soil N dependence requiring low N dose (50 kg/ha) could be rewarding for Andaman and Nicobar Islands climate having high rain fall and low soil fertility and fertilizer use by farmers.
Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume Number 05 (2019) Journal homepage: http://www.ijcmas.com Original Research Article https://doi.org/10.20546/ijcmas.2019.805.114 Can Rice Hybrids Fit Well into Inherently Low Fertile Acidic Soils with Minimal Nitrogen Fertilizer Inputs under Intense Rainfall Receiving Rain Fed Lowlands of Andaman and Nicobar Islands B Gangaiah*, A Sirisha and Sachidananda Swain Division of Natural Resource Management, ICAR-Central Island Agricultural Research Institute, Port Blair, Andaman & Nicobar Islands *Corresponding author ABSTRACT Keywords Rice, Hybrids, Variety, Nitrogen, Net income, Nitrogen use efficiency Article Info Accepted: 10 April 2019 Available Online: 10 May 2019 Rain fed lowland traditional variety rice cultivation in Andaman and Nicobar islands in acidic soils with low inherent fertility is done with minimal use of fertilizer and thus have low yields and profits Use of hybrids and balanced fertilization especially nitrogen (N) may improve the situation In this context, a field study was made during 2016 rainy season to assess the performance of hybrids (including a variety) in main plots and four N rates (0, 50, 100 and 150 kg/ha) as sub-plot treatments Experiment was laid out in split plot design with three replications Results based on grain yield (t/ha) and net income (Rs/ha) revealed that rice hybrid „KPH-459‟ (3.32 t/ha and Rs 14585) and 100 kg/ha N fertilization (3.22 t/ha and Rs.12105) as the best treatments Cultivar and nitrogen interaction indicated that „KPH-459‟ with 50 kg N fertilization is as good as „PR-14019‟, „PR-14112‟ hybrids and better than „WGL-14‟ variety receiving highest N (150 kg) for profits Cultivation of „KPH 459‟ hybrid with 100 kg N gave the significantly higher profits (Rs 29607) than all other cultivars and N combinations Nitrogen uptake followed the trend of grain yields, however all N use efficiency indices (Physiological efficiency, Apparent recovery and Utilization efficiency) except agronomic efficiency have highest values high at 50 kg N N response of rice crop and cultivars was linear (KPH-459‟ and „PR-14019‟ have quadratic response) Replacement of current rice varieties with „KPH459‟ hybrid with high soil N dependence requiring low N dose (50 kg/ha) could be rewarding for Andaman and Nicobar Islands climate having high rain fall and low soil fertility and fertilizer use by farmers 12593 tonnes (t) and productivity of 2.58 t/ha (DOES, 2018) Though these yield was at par with that of country (2.55 t/ha), it was far behind the highest productivity (3.998 t/ha) reported from the state of Punjab (Agricultural Statistics at a Glance, 2017) in the country This huge yield gap (35.5%) was Introduction Rice (Oryza sativa L.) is only the cereal food crop grown in Andaman and Nicobar Islands (ANI) under rain fed situations by transplanting During 2016-17, it was cultivated on 4876 with a production of 975 Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 mainly ascribed to use of traditional varieties that was evident from the fact that 70% of rice acreage is under long duration, photosensitive variety „C-14-8‟ (Subramani et al., 2014) Several high yielding varieties (HYV) are bred locally and popularized among stakeholders in the islands (Singh et al., 2014) besides their introductions from main land states with similar ecology Hybrids development in place of HYV was taken up in the country in 1989 that resulted in release of first hybrid in 1995 and by 2016, 90 hybrids were released in the country (DRD, 2018) These hybrids spread on m (Raja, 2016) were estimated to have pushed up yields by 18.13% in Uttar Pradesh (Singh et al., 2009) and India (FAO, 2014) Thus rice hybrids introduction merits consideration in islands too For realizing genetic potential of HYV and hybrids, adequate and balanced fertilization is necessary as every tonne of rice grain produced on an average removes 20-321.5 kg/ha of N-P-K (Dobermann et al., 1998) Paddy soils of ANI are acidic, saline (acidic-saline, acid-sulphate-saline soils etc.) and are deficit in primary nutrients of NPK (Singh et al., 1988) However, fertilizer use is low and mostly confined to vegetable and fruit crops During 2016-17, 1682 t of NPK fertilizers were used in the islands (DOES, 2017) at an average rate of 41 kg/ha (19.021.4-0.6 kg N-P-K) of cultivated area This low use of N as against the optimum dose 100 kg (Damodaran et al., 2012) calls for use of suitable alternative management approaches In this context, hybrids with vigorous root density (Zhang et al., 2009) relying more on soil N (Hunag et al., 2017) than the fertilizer N may come in handy and should be explored in islands High rain fall received during rice crop season not only constrains top dressing of N but also its efficacy by way of runoff water induced losses Studies on relative performance of hybrids and their N requirements are yet to be attempted in the islands and in this context a study was made to find out the cultivars and nitrogen interactions for the enhancing the rice production Materials and Methods A rain fed lowland transplanted rice experiment was carried out during JulyNovember, 2016 at the Bloomsdale research farm, ICAR- Central Island Agricultural Research Institute, Andaman & Nicobar Islands, India The experimental clay loam soil collected from -20 cm depth in June, 2016 was analysed as per Singh et al., (2005) The analysis revealed that slightly acidic (6.3 pH), non-saline (ECe: 0.55 dS/m) soil with 6150 kg/ha of organic carbon was rated low for available N-P-:K (254-108-129 kg/ha).The experiment was laid out in split plot design (SPD) with three replications Main plot treatments consisted of eight rice cultivars i.e.7 hybrids and a high yielding variety (Table 1) while in sub-plot, four nitrogen rates (0, 50, 100 and 150 kg/ha) representing 0, 50, 100 and 150% of recommended dose of rice crop were allocated Nitrogen fertilizer as prilled urea (46.4% N) was given in three equal splits on 5th, 27th and 47th day after transplanting (DAT) rice A sub-plot size of m x m was used A m buffer channel between sub-plots on all sides with a 30 cm height soil levee and m alleys of bunds and a channel between replications have effectively contained the inter-plot movement of N Irrigation water was also applied to each sub plot separately The experimental plot uniformly received 60 kg/ha each of P2O5 and K2O as single super phosphate (16% P2O5) and potassium chloride (60% K2O) applied in last puddling The experimental soil was puddle thrice with power tiller in standing water Soil was allowed to settle for a day, was manually levelled and experimental lay out was done Thirty day old nursery grown healthy seedlings were transplanted in main field on 3rd August, 2016 with 1-2 seedlings/ 976 Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 hill at 20 cm x 15 cm spacing The crop was grown under rain fed conditions with supplemental irrigation and faced no moisture stress during its life cycle Pre-emergence application of pendimethalin 38.7% CS @ 0.75 kg a.i/ha immediately after transplanting and two manual weeding on 25 and 45 DAT have effectively taken care of weed pressure Nitrogen top dressing succeeded two manual weedings and field was dewatered prior to N application and re-watered two days later Plant height (cm) of 10 randomly selected hills from ground to tip of the top most leaf was measured and for the same plants panicles were counted treatment wise prior to harvest These hills were harvested at cm above the ground level and weight was recorded (g) Grains were separated by hand and counted manually Grains/panicle was arrived as ratio of total grains / panicle number Grain and straw was oven dried for bringing down the moisture contents to 14 and 10% and dry weight was recorded Harvest index was estimated as ratio of weight of 10 hills grain (14% moisture) to weight of straw (10% moisture) + grain Weight of 1000 grains (14% moisture) was recorded and reported as test weight (g) Crop was harvested and biomass yield (kg/plot) was recorded Biomass was sun dried for two days and threshed by manually operated pedal thresher to separate grain Grain yield was recorded plot wise Grain and straw yields were adjusted to 14 and 10% moisture level and their total weight is taken as biomass yield /plot From plot yields, per yield was estimated Nitrogen (N) concentration of grain and straw was estimated as per procedures of Singh et al., (2005) and uptake (kg/ha) was calculated as product of grain/ straw yield (kg/ha) x nutrient concentration (%) / 100 Nitrogen use efficiencies were calculated as per Fageria et al., (2011) Nitrogen harvest index was estimated as grain uptake / biomass uptake x 100 Economics were estimated based input prices of market and output price of rice grain as announced by Government of India as minimum support price (Rs 14,700/t, 2016-17) and assumed straw price of Rs 2,000/t Benefit Cost Ratio (BCR) was worked out as ratio of gross income {grain yield (t/ha) x 14700 +straw yield (t/ha) x 2000} to cost of cultivation (Rs/ha) A fertilizer N price of 12.87/ kg was used The analysis of variance was done in Split Plot Design and significance of treatment differences was compared by critical difference (CD) values at 5% level of significance (P=0.05) and statistical interpretation of treatments was done as per Gomez and Gomez (1984) Results and Discussion Weather during study period Weather data during the experiment period was stressful for water with low rains in August and excess rain in September months (Figure 1) A rain fall of 179.4 cm was received in 59 rainy days Rain fall of November (16.82 cm in rainy days) was not much useful to the crop, as it coincided with crop maturity period A mean maximum and minimum temperature of 30.6 and 24.70C and a mean relative humidity of 75- 90% was recorded at the Indian Meteorological Department (IMD) weather station at Port Blair during crop cycle (August-November) Crop required irrigations during August, October months to maintain 3-5 cm standing water and were provided through running stream water Biotic pressures (pests & diseases and weeds) were taken care through use of plant protection measures and manual / herbicidal weeding measures Recommended P and K fertilizers application uniformly to crop has excluded their stress also Thus any difference in crop performance was solely ascribed to cultivars (hybrid/ variety), nitrogen fertilization and their interaction The results of study were presented for 977 Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 cultivar & nitrogen followed by their interaction for grain yield and income Each successive increase of 50 kg N dose from to 100 kg/ha has significantly increased the grain and biological yield of rice (Table 2) However, harvest index has increased with 100 kg N dose over control only Nitrogen fertilization on an average has increased grain and biological yields by 70.9 and 40.2% over no N control This increase (%) in grain yield was 43.0, 58.9 and 0.01% with 50, 100 and 150 kg N dose over its immediate preceding dose Grain yield exhibited quadratic response as determined by regression equation: y=1.375 + 0.522x (y: yield in t/ha and x: N dose kg/ha) with a R2 value of 0.900 However, quadratic equation (y=0.475 + 1.422x – 0.18x2) has better explained the yield response with high R2 values (0.985) Cultivar and nitrogen Plant height and yield attributes Rice cultivars and N dose have resulted in bringing vast differences in plant height and yield attributes (Table 1) Rice hybrid „KPH459‟ has produced significantly taller plants than „PR-14112‟, „DRRH-3‟ hybrids and WGL-14 and was at par with other hybrids „DRRH-3‟ has the shortest plants Significantly higher number of panicles/m2 (268) and grains/panicle (135) were recorded with KPH-459 However, grains/ panicle of KPH-459 were at par with HRI-186 DRRH-3 and WGL-14 that has lowest panicles/m2 and grains/ panicle stood at the top (23.70 g) and bottom (16.58 g) for test weight, respectively Nitrogen uptake and use efficiency Nitrogen concentration of grain and straw were markedly altered by N fertilization and cultivars have no influence (Figure 2) Plant height and panicle/m2 increased significantly with each successive increase of 50 kg N from to 100 kg N/ha Further increase in N to 150 kg failed to enhance these attributes markedly However, grains/ panicle increased significantly only up to 50 kg N application over control and test weight remained unaffected by N dose Rice cultivars differed for grain, biomass (grain + straw) N uptake, N use efficiency indices (Table 3) and N dose too have marked impact on above parameters Rice hybrid „KPH-459‟ has significantly higher N uptake, NHI, AE, AR and UE values However, for PE, „HRI-186‟ hybrid stood at the top and excelled „KPH-459‟ Cultivars „DRRH-3‟ and „WGL-14‟ with at par N uptake and use efficiency values (except PE and AR) stood at the bottom and have statistically lower values than all other hybrids Grain, biomass yield and harvest index Biomass, grain yield and harvest index were markedly improved due to N dose and cultivars too differed greatly for these attributes (Table 2) Rice hybrid „KPH-459‟ has significantly higher grain, biomass yield and harvest index values (3.32, 8.43 t/ha and 39.4) than all other cultivars All hybrids except „DRRH-3‟ hybrid have exceeded HYV „WGL-14‟ for grain and biomass yield For lower biomass yields, „PR-14112‟ joined „WGL-14‟ and „DRRH-3‟ group with at par values DRRH-92 and HRI-186 with at par yield among themselves are the second best grain yielders Application of 50 and 100 kg N has markedly improved N concentration of grain and stover over no N control Biomass N uptake (kg/ha) on an average was increased by 71.6% with N application as compared to its control Nitrogen harvest index increased significantly with 50 N applications over no N control (46.2) and all N fertilised plots have at par NHI values Except AE, all other N use 978 Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 indices (PE, AR and UE) have significantly higher values at 50 kg N dose over control AE attained highest values at 100 kg N Nitrogen response was linear (y=1.375 + 0.522x; R2: 0.900) profitable Application of 100 kg N was essential to realise best profits (Rs 12105) and BCR (1.26) values Economics Grain yield Economics (Rs/ha) of rice cultivation was significantly altered by cultivars and N fertilization and varied among cultivars (Table 4) The differences in cost of cultivation between a hybrid and variety (Rs 3600/ha) came from higher seed cost of hybrid as compared to a variety (Rs 42432) Hybrid seed price (Rs/kg) was 6.67 times that of a variety (Rs 30/kg) and 20 kg seed was used in both of them Grain yield and net income of rice differed greatly due to cultivar and N fertilization interaction (Table 5) Cultivar X nitrogen Hybrids grain yields got magnified with N fertilization with best yield response at 100 kg N fertilization Rice hybrids „KPH-459‟, „PR14019‟ showed decline in yields with 150 kg N as compared to 100 kg indicating their response is in between these two doses In other cultivars, yield is increasing slightly and net income will be the best indicator At low as well as recommended dose of N (50 and 100 kg), „KPH-459‟ hybrid is inevitable choice On income side, the differential grain and straw yields of cultivars translated into net income changes „KPH-459‟ hybrid had significantly higher net income (Rs.14585) than all other cultivars and thus has higher BCR (1.32) At the current study yields, „DRRH-3‟ hybrid cultivation was a loss making proposition „WGL-14‟ variety and „PR-14019‟ hybrid cultivation may also be uneconomical as their net income is < CD value „DRRH-92‟ and „HRI-186‟ hybrids are the second best economically remunerative rice cultivars Other two hybrids (PR-14111 and PR-14112) too have small profit margins Benefit cost ratio (BCR) followed the net income trend Net income Yield differences of cultivars when seen from net income point of view entirely a new picture emanated (Table 6) At no N and 50 kg N rate, rice cultivation is loss making proposition irrespective of cultivar (except hybrids at 50 kg N i.e KPH-459, DRRH-92 and PR-14019) Hybrid „KPH-459‟ with 100 kg N dose remained the most remunerative treatment (Rs 29607) Each 50 kg increase in N rate has increased the cost of cultivation by Rs.944 Nitrogen fertilization on an average has increased the gross and net income by 62.9 and 44.5% as compared to no N control (Rs 33565) However, on account of low grain and straw yields, no N control has recorded net losses (Rs.-10539) Further, the yields obtained with 50 kg N too have small profits (Rs 1197) that are < CD values and thus is also not Increasing N dose beyond 100 kg/ha has reduced the net income of „KPH-459‟ and „PR-14019‟ Nitrogen response of cultivars varied greatly All cultivars except „KPH459‟ and „PR-14019‟ have linear response to the N fertilization rate (Table 7) However, the linear responses of cultivars were better explained by quadratic equations than linear one 979 Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 Table.1 Plant height and yield attributes of rice as affected by cultivars and nitrogen rate Rice hybrid / variety* (C ) Panicles/ m2 Grains /panicle Test weight (g) Plant height (cm) DRRH-92 HRI-186 KPH-459 PR-14019 PR-14111 PR-14112 DRRH-3 WGL-14* CD (P=0.05) Nitrogen rate (kg/ha): N 251c 237b 268d 242bc 241bc 232b 216a 218 a 13.3 106ab 130c 135c 103ab 108b 109b 98a 107ab 9.6 19.98bc 21.31d 19.28bc 18.97b 19.02bc 20.13c 23.70e 16.58a 1.14 106.0abc 107.1bc 110.2c 105.9abc 105.4abc 104.8ab 100.4a 102.0ab 5.08 50 100 150 CD (P=0.05) Interaction (C x N) 167a 235b 274c 275c 10.0 NS 99.7 a 108.3 b 113.2 b 114.8 b 7.22 NS 19.72 a 19.85 a 19.92 a 19.97 a NS NS 89.9a 103.4b 113.2c 116.4 c 3.82 NS *Same alphabet in superscript denotes at par values Table.2 Grain and biomass yield and harvest index of rice as affected by cultivars and nitrogen rate Rice hybrid / variety* (C ) DRRH-92 HRI-186 KPH-459 PR-14019 PR-14111 PR-14112 DRRH-3 WGL-14* CD (P=0.05) Nitrogen rate (kg/ha) Yield (t/ha) Grain Biomass 2.90d 7.96d 2.93d 8.02d e 3.32 8.43e 2.56c 7.52c 2.66c 7.42bc c 2.62 7.16ab 2.10a 6.88a 2.34b 6.89a 0.128 0.293 1.75 a 2.50 b 3.22c 3.25c 0.096 0.225 50 100 150 CD (P=0.05) Interaction (Cultivar x N) 6.05 a 7.73 b 8.72c 8.99d 0.220 0.512 *Same alphabet in superscript denotes at par values 980 Harvest index 36.4bcd 36.5bcd 39.4d 34.0abc 35.8bcd 36.6bcd 30.5a 34.0ab 4.70 28.9a 32.3b 33.9b 33.2b 3.51 NS Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 Table.3 Nitrogen uptake and use efficiency of rice as influenced by cultivars and N rate Rice hybrid / variety* (C ) DRRH-92 HRI-186 KPH-459 PR-14019 PR-14111 PR-14112 DRRH-3 WGL-14* CD (P=0.05) Nitrogen rate (kg/ha): N 50 100 150 CD (P=0.05) Interaction (C x N) N uptake (kg/ha NHI Nitrogen use efficiency* AE PE AR UE Grain 33.8 34.5 39.4 29.9 30.8 31.7 25.0 27.8 2.41 Grain 64.5 67.4 76.2 60.0 60.6 61.2 53.0 55.2 6.63 52.0 50.6 51.2 49.5 50.2 51.1 46.8 49.8 NS 26.4 31.7 37.6 20.3 23.5 24.5 14.9 18.4 2.10 96.2 108.8 102.9 87.8 88.4 75.0 87.3 72.9 4.02 34.64 36.96 48.51 28.64 25.87 27.39 19.59 23.11 2.673 33.31 40.17 50.30 25.45 22.86 20.57 17.12 16.87 3.658 18.7 29.2 38.7 39.9 1.81 NS 40.5 57.8 72.9 78.0 4.99 NS 46.2 50.4 53.0 51.0 3.5 NS α 14.8 29.3 29.9 1.58 NS α 92.6 88.7 88.4 3.02 NS α 34.47 32.30 24.96 2.01 NS α 32.67 29.71 22.62 2.75 NS *NHI: Nitrogen harvest index; AE: Agronomic efficiency (kg grain/ kg N applied): PE: Physiological efficiency (kg biomass/ kg N uptake): AR: Apparent recovery (%); UE: Utilization Efficiency (kg/kg) Table.4 Economics of rice cultivation as influenced by cultivars and nitrogen rate Rice hybrid / variety* (C ) Economics (Rs/ha) DRRH-92 HRI-186 KPH-459 PR-14019 PR-14111 PR-14112 DRRH-3 WGL-14* CD (P=0.05) Nitrogen rate (kg/ha) : N 50 100 150 CD (P=0.05) Interaction (C x N) Gross returns Cost of cultivation Net returns Benefit Cost Ratio 52771d 53813d 60617e 47474c 49014c 47910c 39740a 43643b 2541 46032b 46032b 46032b 46032b 46032b 46032b 46032b 42432a - 6739d 7781d 14585e 1442b 2982c 1878bc -6292a 1211b 1600.0 1.15bc 1.17c 1.32d 1.03b 1.06b 1.04b 0.86a 1.03b 0.106 33565 a 46390 b 58194 c 59415 c 1910.5 44166 a 45110 b 46053 c 46997 d - -10539 a 1197 b 12105 c 12402 c 1203.0 2812.5 0.76 a 1.03b 1.26c 1.26c 0.080 *Same alphabet in superscript denotes at par values 981 Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 Table.5 Grain yield (t/ha) of rice as influenced by cultivar X nitrogen rate Rice hybrid / variety* Nitrogen rate (kg/ha) 50 100 150 1.91c 2.70d 3.43d 3.56d DRRH-92 1.74bc 2.45bc 3.75e 3.78d HRI-186 c e f 1.91 3.02 4.25 4.10e KPH-459 bc cd c 1.80 2.65 2.95 2.84b PR-14019 1.78bc 2.40b 3.14c 3.32c PR-14111 abc c c 1.70 2.53 3.09 3.16c PR-14112 a a a 1.54 1.93 2.44 2.49a DRRH-3 ab b b 1.65 2.28 2.69 2.74b WGL-14* V at same N V at different N 0.225 0.246 CD (p=0.05) *Same alphabet in superscript denotes at par values for V at same N Table.6 Net income (Rs.) of rice as influenced by cultivar X nitrogen rate Rice hybrid / variety* Nitrogen rate (kg/ha) 50 100 150 -9124 3814b 15206c 17060 a DRRH-92 -11908 -201 21558d 21676 e HRI-186 c e -8783 10611 29607 26906 f KPH-459 ab b -10143 3281 7305 5327 a PR-14019 b -10104 -700 9935 12797 c PR-14111 -11302 751a 8380 ab 9685 b PR-14112 -14510 -8795 -1155 -704 DRRH-3 -8441 816a 6000 a 6471 a WGL-14* V at same N V at different N 2812.5 3075.0 CD (p=0.05) *Same alphabet in superscript denotes at par values for V at same N Table.7 Yield response functions of rice cultivars to nitrogen Linear Y= 0.568x + 1.48 (0.928) Y= -0.165x2 + 1.393x + 0.655 (0.991) Best response function (based on R2) Quadratic HRI-186 Linear Y= 0.742x + 1.075 (0.905) Y= -0.17x2 + 1.592x + 0.225 (0.943) Quadratic KPH-459 PR-14019 PR-14111 PR-14112 DRRH-3 WGL-14* Nitrogen response Response equations (R2 values) Rice hybrid / variety* DRRH-92 Quadratic Quadratic Linear Linear Linear Linear Linear Quadratic - Quadratic Quadratic Y= -0.315x + 2.355x + 0.205 (0.968) - Y= -0.315x + 1.542x + 0.505 (0.998) Y= 0.952x + 1.32 (0.952) Y= 0.494x + 1.385 (0.892) Y= 0.336x + 1.26 (0.925) Y= 0.368x + 1.42 (0.888) Y= -0.11x + 1.086x + 0.77 (0.984) Y= -0.19x + 1.444x + 0.435 (0.998) Quadratic Quadratic Quadratic Y= -0.085x + 0.761x + 0.835 (0.972) Y= -0.145x + 1.093x + 0.695 (0.998) y: yield in t/ha and x: N dose kg/ha 982 Quadratic Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 Fig.1 Weather data at study site (rainfall, rainy days on y1 and temperature on y2 axis) Fig.2 Nitrogen concentration (%) of rice grain and straw under varying nitrogen rates This was because the yield increases with 150 kg over 100 kg N was marginal but N dose increased constantly by 50 kg However, optimum dose can‟t be worked out for these cultivars due to linear response (Table 7) Rice cultivars produced plants with a mean height of 105.7 cm that have 238.0 panicles/ m2, each panicle had 112 grains and grains have a test weight of 19.87 g „KPH-459‟ hybrid with 30 and 23 more number of 983 Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 panicles/m2 and grains/ panicle than the mean values has resulted in 23.9 and 18.2% higher grain and straw yield than mean yield of 2.68 and 5.00 t/ha The higher yields together have resulted in 2.85 times higher net income than the mean (RS 3791) Similar differences in performance of hybrid over variety reported by Siva Prasad et al., (2017) and Banerjee et al., (2019) corroborate the current research findings location The NHI of current study is quiet lower than the reported values of 64% by Fageria and Baligar (2001) for lowland rice All nitrogen use efficiency indices are best with 50 kg N application; however, AE increased up to 150 kg Decrease in PE was ascribed lesser increases in N uptake by biomass than the increase in N dose Decrease in AR was ascribed to inability of rice roots to capture more N supplies when high doses of N was given Apparent Recovery of nitrogen was highest with 50 kg (34.47%) and decreased with increased N rate to the lowest of 24.96 with 150 kg N UE a product of AR and PE followed their trend Current experimental soil was low in available N (258 kg/ha) and was subjected to heavy rains in September month (99.2 cm) that have made the third split dose of N less useful In the above scenario, rice crop N response was captured Nitrogen nutrition has contributed to formation of more number of tillers and their transformation into panicles /m2 and panicles have greater number of grains Application of 100 kg N has improved the panicles/m2 and grains / panicle by 12.7 and 6.3% over their mean (mean of N levels) values of 238 and 112 On account of above increases in yield attributes along with meagre increases (0.05 g) of test weight over mean (19.87 g) together have resulted in 20.15% higher grain yield than the mean (2.68 t/ha) The increase in straw yield over mean yield (5 t/ha) was 8.6% The above grain and straw yield increases have got translated into 2.19 times more net income (Rs 12105) than the mean of Rs 3791 Nitrogen dose response of rice crop up to 100 kg N of this study are quite lower than that reported (184.9 kg/ha) by Yadav et al., (2016), but the trend is similar Nitrogen concentration of both grain and straw was altered by N fertilization on account of low soil N status that along with higher grain and straw yields has increased N uptake substantially due to N application and cultivars A mean NHI of 50.15 was recorded in this study A NHI of 53 is required for best performance and these values are obtained with 100 kg N application at the experimental Interaction effect of cultivar and N indicates that KPH-459 followed by DRRH-92 hybrids are the first and second best performers at low N fertilization (50 kg) „KPH-459‟ hybrid with 100 kg N is the best combination for yield and incomes At 100 kg N dose, the place of „DRRH-92‟ was taken by „HRI-186‟ hybrid „WGL-14‟ variety was a poor performer and even with highest N dose (150 kg) its performance can‟t match with „KPH-459‟, „DRRRH-92‟ and „PR-14019‟ receiving 50 kg N Hybrids superiority at low N of the current study may be ascribed to their larger, deeper, and more vigorous root system (Zhang et al., 2009) of hybrid that might have enabled it to draws more soil N (Hunag et al., 2017) while fertilizer N contributions remained similar for a hybrid and high yielding variety From the above study it is concluded that „KPH-459‟ rice hybrid and N fertilization of 100 kg/ha are best for grain yield and economics Cultivar and nitrogen interaction indicated that scope lies for improving rice productivity with low (50 kg) N fertilization by choosing „KPH 459‟ hybrid as compared to others Such interactions need to be explored in islands for overcoming the low N 984 Int.J.Curr.Microbiol.App.Sci (2019) 8(5): 975-986 input farming of Andaman and Nicobar Islands subjected to heavy rains that derails N response DOES (Directorate of Economics and Statistics) 2018 Agriculture: Major Crops in A&N Islands DOES, Andaman and Nicobar Administration, Port Blair Fageria, N K and Baligar, V C 2001 Lowland rice response to nitrogen fertilization Communications in Soil Science and Plant Analysis 32(9): 1405-1429 Fageria, N K., Baligar, V C and Jones, C A 2011 Growth and mineral nutrition of field crops 3rd Edition, CRC Press, Boca Raton Gomez, K A and Gomez, A A 1984 Statistical Procedures for Agricultural Research John Wiley and Sons, Inc London, UK, (2nd Ed) Huang, M., Peng Jiang, ShuanglüShan, Wei Gao, Guohui Ma, Yingbin Zou, Norman Uphoff and Longping Yuan 2017 Higher yields of hybrid rice not depend on nitrogen fertilization under moderate to high soil fertility conditions Rice (N Y): 10: 43 Raja, 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Sirisha and Sachidananda Swain 2019 Can Rice Hybrids Fit Well into Inherently Low Fertile Acidic Soils with Minimal Nitrogen Fertilizer Inputs under Intense Rainfall Receiving Rain Fed Lowlands of Andaman and Nicobar Islands Int.J.Curr.Microbiol.App.Sci 8(05): 975-986 doi: https://doi.org/10.20546/ijcmas.2019.805.114 986 ... Sirisha and Sachidananda Swain 2019 Can Rice Hybrids Fit Well into Inherently Low Fertile Acidic Soils with Minimal Nitrogen Fertilizer Inputs under Intense Rainfall Receiving Rain Fed Lowlands of Andaman. .. of Andaman and Nicobar Islands subjected to heavy rains that derails N response DOES (Directorate of Economics and Statistics) 2018 Agriculture: Major Crops in A&N Islands DOES, Andaman and Nicobar. .. the islands and in this context a study was made to find out the cultivars and nitrogen interactions for the enhancing the rice production Materials and Methods A rain fed lowland transplanted rice